Image sensors are semiconductor devices that convert an optical image into an electric signal. Examples of image sensors are a charge coupled device (CCD) and a complementary metal-oxide-silicon (CMOS) image sensor.
The CCD includes metal-oxide-silicon capacitors that are formed very close to one another, wherein charge carriers are stored and transported into the metal-oxide-silicon capacitors. The CMOS image sensor functions based on CMOS technology, which uses control circuits and signal processing circuits as peripheral circuits, employs a switching method in which MOS transistors are formed corresponding to the number of pixels and the output is detected using the MOS transistors.
The CMOS image sensor may be driven more easily than the CCD, and may be advantageous in terms of minimized modules because signal processing circuits can be integrated into one chip, and thus, a system-on-chip may be realized. Accordingly, CMOS image sensors are widely used in mobile phones, cameras for personal computers, and electronic appliances.
FIG. 1 is a cross-sectional view of a conventional 3D integration CMOS image sensor.
Referring to FIG. 1, the conventional 3D integration CMOS image sensor includes a light receiving unit including a photo diode (PD) 10 formed on a substrate, a wiring line layer 20, a color filter array (CFA) 30, and a micro-lens 40. As such, the wiring line layer 20 comprises a plurality of wiring lines M1 through M4 and transparent insulating layers disposed between the CFA 30 and the PD 10.
The manufacturing method of the conventional 3D integration CMOS image sensor includes a back end of line (BEOL) method, that is, a metal line method that is similar to that in a manufacturing process of a semiconductor device. In this case, different insulating materials can be used for forming a pre-metal dielectric (PMD), an inter-metal dielectric (IMD), and a passivation layer. Thus, light may be diffused at interfaces between the pre-metal dielectric (PMD), inter-metal dielectric (IMD), and passivation layers, and as such, the photosensitivity of the conventional 3D integration CMOS image sensor may be decreased.
Also, due to the different refractive indices of the different insulating layers, the photosensitivity of the conventional 3D integration CMOS image sensor may be decreased due to the refraction of light. In addition, since the metal wiring lines M1 through M4 are formed and the transparent insulating layers are planarized after forming a photo diode when manufacturing the conventional 3D integration CMOS image sensor, defects due to these processes may occur.
In cases where a plurality of transistors are arranged around the photo diode for signal processing and control, the surface area for receiving light for each pixel may be reduced. In other words, saturation of a light-receiving region of each pixel may be reduced. Accordingly, noise may be increased, and a danger of losing images according to such noise increases, and thereby, deteriorating image quality.